Urolithiasis can be defined as the presence of macroscopic mineralisation within the urinary tract, ranging in size from sand particles to radiographically obvious uroliths. Uroliths of a variety of different mineral types have been identified within the canine and feline lower urinary tract, such as struvite, calcium oxalate, calcium phosphate, uric acid and urates.
Lower urinary tract diseases associated with mineral precipitation are important clinical problems in dogs and cats. Whilst a number of different minerals may be present in the lower urinary tract, two are of particular importance; (a) struvite (magnesium ammonium phosphate) and (b) calcium oxalate. Precipitation of these minerals may be associated with disease in animals such as dogs, cats and humans when it results in urolithiasis.
Urolithiasis continues to be an important clinical problem in dogs. Struvite (magnesium ammonium phosphate) has been the most numerically important type of urolith found in dogs. Recent data suggest that the number of calcium oxalate uroliths is increasing in dogs, and that uroliths of this type may now be of equal or greater importance than struvite, particularly in certain breeds. The majority of dogs with struvite urolithiasis have an associated urinary tract infection with urease-producing bacteria, such as staphylococci or Proteus spp. Hydrolysis of urea by the enzyme urease, ultimately results in the formation of ammonia and carbonate which creates an increasingly alkaline environment in the urine. These conditions are ideal for the development of struvite uroliths, but also favour the formation of a number of other urolith types including calcium carbonate and apatite. Thus, in the majority of dogs with struvite urolithiasis appropriate anti-microbial agents form an essential part of therapy. Usually, once the urinary tract infection has been fully eradicated, the dog will not require any long term dietary management. Nevertheless, a number of canine diets designed as a nutritional aid for dogs which suffer from struvite urolithiasis (such as Hills canine s/d) are on the market. Most pet food diets which are designed as nutritional aids for pets with struvite urolithiasis are contraindicated for use with pets suffering from non-struvite urolithiasis.
Cases of calcium oxalate urolithiasis require surgical removal. Only then are dietary measures adopted to prevent reformation of the urolith. Clearly, it would be advantageous to provide a comestible which is designed for management or prevention of calcium oxalate uroliths, avoiding their initial formation in canine animals.